The article is very short and sweet, and thoroughly explains the problem with 3rd Nephi in light of modern biblical textural criticism. In order for apologists to believe in a literal sermon on the mount, they have to completely reject the near universal scholarly consensus on the creation of the New Testament.
https://www.dialoguejournal.com/wp-cont ... 03_147.pdf
The conclusion of the article is devastating to belief in the events of the Book of Mormon being literal:
The version of the SOM presented in 3 Nephi closely follows the form and arrangement given in Matthew 5-7. The claim on the part of 3 Nephi to represent an independent witness to this teaching of Jesus rests on the assumption that it was Jesus who organized the material into the form in which we now find it in both the gospel of Matthew and 3 Nephi. Current scholarship on Matthew, however, indicates that this is not the case, that indeed Matthew contributed significantly to the shaping of his version of the SOM. If this assessment is correct, it is no longer possible to regard 3 Nephi 12-14 as a record of an actual sermon that was delivered before first-century Nephites by the resurrected Jesus, since Nephi could not have known Matthew. Rather, the 3 Nephi SOM was derived from Matthew (in the particular form given it by the KJV), after which certain minor changes were made with a view toward assimilating it to its New World setting.